PEER-REVIEWED ARTICLE bioresources.com Kuokkanen et al. (2011). “Additives in wood pellets,” BioResources 6(4), 4331-4355. 4331 ADDITIVES IN WOOD PELLET PRODUCTION – A PILOT-SCALE STUDY OF BINDING AGENT USAGE Matti Kuokkanen, a, * Teemu Vilppo, b Toivo Kuokkanen, a Tuomas Stoor, c and Jouko Niinimäki c Finland currently has tremendous enthusiasm to increase decentralised pellet production alongside of large-scale factories. The aim of research is to promote the development of eco-/cost-efficient Nordic wood-based pellet production by means of multidisciplinary research. Using Finnish conifer stem wood (bark-free Scotch pine sawdust and shavings) as a model raw material, the total functionality of a pilot-scale pellet facility combined with an extensive chemical toolbox was tested in this study to promote future development of eco- and cost-efficient wood-based pellet production in both quantitative and qualitative senses. Lignosulphonate, residual potato flour, and potato peel residue were used as adhesive binding agents. A pilot-scale pellet facility was equipped with a data logger for temperature and power measurements. The chemical toolbox included also novel specific staining and optical microscope methods and respirometric BOD Oxitop measurements. The results showed that adhesive binding agents increased the quality of pellets and changed inorganic characteristics, but did not have a significant effect on their calorimetric heat values. Lignosulphonate even increased the rate of production. Valuable information about both the pelletizing process and pellets is necessary in the future when developing good-quality pellets, a prime biofuel, from low-value and/or moist biomass that has undergone a cost-efficient drying process. Keywords: Bioenergy; Wood pellet; Pellet technology; Binding agent; Starch; Lignosulphonate; Biodegradation Contact information: a: Department of Chemistry, University of Oulu, P.O Box 3000, FI-90014, Oulu, Finland; b: School of Forest Sciences, University of Eastern Finland, P.O Box 111 FI-80101, Joensuu, Finland; c: Department of Process and Environmental Engineering, University of Oulu, P.O Box 4300, FI- 90014, Oulu, Finland ; *Corresponding author: matti.kuokkanen@oulu.fi INTRODUCTION Wood pellets are short cylindrical pieces (with a usual diameter of 6 to 10 mm and a length of 10 to 30 mm) which are produced mechanically by compressing a uniform material that has first passed through a hammer mill or mills to provide a homogeneous particle size. This mass is fed to a press where it is pressed through a die with holes of the size required. Typically the diameter of pellets is 8 mm in Nordic Countries, 6 mm in Central Europe (Thek and Obernberger 2004), and sometimes 15 mm and up to 25 mm according to CEN/TS 14961. The high pressure and friction of the press causes the temperature of the wood to increase significantly, slightly plasticizing the lignin in the temperature range 100 to 130 °C (Kaliyan and Vance 2009) and forming a natural 'glue' that holds the pellet together as it cools.